In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), there is a continued desire to reduce the size of structural features. In the microelectronics industry, the desire is to reduce the size of microelectronic devices and/or to provide greater amount of circuitry for a given chip size.
The ability to produce smaller devices is limited by the ability of lithographic techniques to reliably resolve smaller features and spacings. The nature of optics is such that the ability to obtain finer resolution is limited in part by the wavelength of light (or other radiation) used to create the lithographic pattern. Thus, there has been a continual trend toward use of shorter light wavelengths for lithographic processes. Recently, the trend has been to move from so-called I-line radiation (350 nm) to 248 nm radiation.
For future reductions in size, the need to use 193 nm radiation appears likely. Unfortunately, resist compositions at the heart of current 248 nm lithographic processes are typically unsuitable for use at shorter wavelengths.
While a resist composition must possess desirable optical characteristics to enable image resolution at a desired radiation wavelength, the resist composition must also possess suitable chemical and mechanical properties to enable transfer to the image from the patterned resist to an underlying substrate layer(s). Thus, a patternwise exposed positive resist must be capable of appropriate dissolution response (i.e. selective dissolution of exposed areas) to yield the desired resist structure. Given the extensive experience in the lithographic arts with the use of aqueous alkaline developers, it is important to achieve appropriate dissolution behavior in such commonly used developer solutions.
The patterned resist structure (after development) must be sufficiently resistant to enable transfer of the pattern to the underlying layer(s). Typically, pattern transfer is performed by some form of wet chemical etching or ion etching. The ability of the patterned resist layer to withstand the pattern transfer etch process (i.e., the etch resistance of the resist layer) is an important characteristic of the resist composition.
While some resist compositions have been designed for use with 193 nm radiation, these compositions have generally failed to deliver the true resolution benefit of shorter wavelength imaging due to a lack of performance in one or more of the above mentioned areas. For example, there is a desire for resist compositions exhibiting improved development characteristics (e.g., resolution, development speed, contrast, shrinkage, etc.), improved etch resistance, and improved lithographic process window. There is especially a desire for resist compositions having improved image stability and reduced sensitivity to fluctuations in post-exposure bake.
The invention provides resist compositions which are capable of high resolution lithographic performance using 193 nm imaging radiation (and possibly also with other imaging radiation). The resist compositions of the invention possess an improved combination of improved development characteristics, improved etch resistance, and/or reduced post-exposure bake sensitivity needed to provide pattern transfer at very high resolutions which are limited only by the wavelength of imaging radiation.
The invention also provides lithographic methods using the resist compositions of the invention to create resist structures and methods using the resist structures to transfer patterns to an underlying layer(s). The lithographic methods of the invention are preferably characterized by the use of 193 nm ultraviolet radiation patternwise exposure.
In one aspect, the invention encompasses a resist composition comprising:
(a) an acid-sensitive imaging polymer, and
(b) a radiation-sensitive acid generator, the imaging polymer comprising:
i) cyclic olefin monomeric units each having a pendant acid-labile moiety that inhibits solubility in aqueous alkaline solutions,
ii) cyclic olefin monomeric units each having a pendant lactone moiety, and
iii) cyclic olefin monomeric units each having a pendant fluoroalcohol moiety.
The lactone moiety is preferably present as a pendant lactone ester.
In another aspect, the invention encompasses a method of forming a patterned material structure on a substrate, the method comprising:
(A) providing a substrate with a layer of the material,
(B) applying a resist composition to the substrate to form a resist layer on the substrate, the resist composition comprising (a) an imaging polymer, and (b) a radiation sensitive acid generator, the imaging polymer comprising monomer units having a group pendant from a polymerizing portion of the monomer, the pendant group containing a remote acid-labile moiety;
(C) patternwise exposing said substrate to radiation whereby acid is generated by said acid generator in exposed regions of said resist layer by said radiation,
(D) contacting said substrate with an aqueous alkaline developer solution, whereby said exposed regions of said resist layer are selectively dissolved by said developer solution to reveal a patterned resist structure, and
(E) transferring resist structure pattern to said material layer, by etching into said material layer through spaces in said resist structure pattern.
Preferably, the radiation used in step (B) in the above method is 193 nm ultraviolet radiation. The material to be patterned is preferably selected from the group consisting of organic dielectrics, semiconductors, metals, and ceramics.
These and other aspects of the invention are discussed in further detail below.